Turbulent-boundary-layer trailing-edge noise reduction technologies including porous materials

Noise reduction is one of the major challenges to the societal acceptance of wind turbines. Aerodynamic noise sources are the dominant ones, assuming that mechanical noise can be reduced by correct insulation and periodic maintenance of the gearbox and drive train and by adding insulating material in the wind-turbine nacelle. The dominant...

A wavelet-based separation method for tonal and broadband components of low Reynolds-number propeller noise

Propeller noise generally exhibits a rich mixture of tonal and broadband components related to different physical mechanisms. Specifically, the tones are characterized by having deterministic and persistent characteristics, while the broadband counterpart has random behaviour. The separation is essential for the experimenters as they provide...

A Numerical Study on Aircraft Noise Mitigation Using Porous Stator Concepts

This manuscript presents the application of a recently developed noise reduction technology, constituted by poro-serrated stator blades on a full-scale aircraft model, in order to reduce rotor-stator interaction noise in the fan stage. This study was carried out using the commercial lattice Boltzmann solver 3DS-SIMULIA PowerFLOW. The simulation...

Small-Scale Rotor Aeroacoustics for Drone Propulsion: A Review of Noise Sources and Control Strategies

In the last decade, the drone market has grown rapidly for both civil and military purposes. Due to their versatility, the demand for drones is constantly increasing, with several industrial players joining the venture to transfer urban mobility to the air. This has exacerbated the problem of noise pollution, mainly due to the relatively lower...

A physics-based description and modelling of the wall-pressure fluctuations on a serrated trailing edge

A physical description of the flow mechanisms that govern the distribution of the wall-pressure fluctuations over the surface of a serrated trailing edge is proposed. Three main mechanisms that define the variation of turbulent pressure fluctuations across the serrated edge are discussed and semi-empirical models are formulated accordingly....

Aeroacoustics of sawtooth trailing-edge serrations under aerodynamic loading

The impact of aerodynamic loading on a serrated trailing edge is studied experimentally. Aerodynamic and acoustic measurements are conducted on a sawtooth-shaped trailing edge, retrofitted to a flat plate featuring a trailing-edge flap, and placed at incidence to the free-stream flow. The turbulent flow across the trailing edge is inspected...

Measurement techniques for aeroacoustics: From aerodynamic comparisons to aeroacoustic assimilations

Sustainability has encouraged studies focusing on lowering the aeroacoustic impact of new aerodynamically optimized mechanical systems for several applications in wind-energy, aviation, automotive and urban air-mobility. The deployment of effective noise-reduction strategies starts with a deep understanding of the underlying mechanisms of...

Numerical analysis of a 3-D printed porous trailing edge for broadband noise reduction

Lattice Boltzmann simulations were carried out to investigate the noise mitigation mechanisms of a 3-D printed porous trailing-edge insert, elucidating the link between noise reduction and material permeability. The porous insert is based on a unit cell resembling a lattice of diamond atoms. It replaces the last 20 % chord of a NACA 0018 at...

Noise reduction mechanisms of an open-cell metal-foam trailing edge

Open-cell porous materials have been reported as a promising concept for mitigating turbulent boundary-layer trailing-edge noise. This manuscript examines the aeroacoustics of a porous trailing edge to study its noise reduction mechanisms. Numerical investigations have been carried out for a NACA 0018 aerofoil with three different types of...

Jet-installation noise and near-field characteristics of jet-surface interaction

The link between jet-installation noise and the near-field flow features of the corresponding isolated jet is studied by means of lattice-Boltzmann numerical simulations. The computational set-up consists of a flat plate placed in proximity to a jet, replicating the interaction benchmark study carried out at NASA Glenn. Installation effects...

Noise reduction mechanisms of sawtooth and combed-sawtooth trailing-edge serrations

Trailing-edge serrations are add ons retrofitted to wind-turbine blades to mitigate turbulent boundary-layer trailing-edge noise. This manuscript studies the physical mechanisms behind the noise reduction by investigating the far-field noise and the hydrodynamic flow field. A conventional sawtooth and a combed-sawtooth trailing-edge serration...

Benefits of curved serrations on broadband trailing-edge noise reduction

Far-field noise and flow field over a novel curved trailing-edge serration (named as iron-shaped serration) are investigated. Spectra of the far-field broadband noise, directivity plots and the flow-field over the iron-shaped serration are obtained from numerical computations performed using a compressible Lattice-Boltzmann solver. The new...

Concave serrations on broadband trailing edge noise reduction

The far-field noise and flow field of a novel curved trailing-edge serration (i.e. iron-shaped) are investigated. Spectra of the far-field broadband noise, directivity plots and the flow-field over the iron-shaped serration are obtained from numerical computations performed using a compressible Lattice-Boltzmann solver. The new design is...

Experimental investigation of the flow inside a saxophone mouthpiece by particle image velocimetry

An experimental study of the flow inside a saxophone mouthpiece in playing conditions is carried out by means of particle image velocimetry at high acquisition rate. Planar velocity measurements on the midsection of a Plexiglas tenor saxophone mouthpiece are performed, respectively, in the mouthpiece baffle and in the reed channel. Sequences of...